210 MORPHOLOGY AND EVOLUTION
When the lumbar arteries arose as median unpaired vessels, as they did in the three Chimpanzees, they bifurcated later; in one animal, as in the Gorilla described by Eisler (442^, the fourth artery is an ilio-lumbar artery. In the Gorilla, the middle sacral artery gives off the first sacral artery, and divides into two lateral sacral arteries. Occasionally it is double.
Sometimes the spermatic of the left side arises from the left suprarenal, a condition which approaches the state in the female Chimpanzee described above.
The Cceliac Axis (fig. 44, C.Ax.) arises immediately above the pancreas, and divides into hepatic, splenic and coronary arteries. In some Chimpanzees it also gives off a pyloro-duodenal artery.
The hepatic artery (H.A.) is related to other structures in the front of the foramen of "Winslow as in Man. In the Chimpanzee it bifurcates; one half i,a'» divides into two vessels, which enter the portal fissure of the liver ; the other half (b) gives off a cystic artery (c.aJ to the gall-bladder, and divides into two branches which enter the right and left lobes of the liver. The parent artery gives off a trunk which divides into three vessels : the right gastric artery (r.g.a./. which anastomoses with the left gastric artery; pyloro-duodenal vessels (p.d.v.), which anastomose with the pyloro-duodenal branch of the cceliac axis; and the right gastro-epiploic artery (r.g.e.a.)j which anastomoses with branches of the splenic artery in the great omentum.
The splenic artery (S.A.) gives branches to the stomach, spleen and pancreas. Its branches form the left gastro-epiploic artery (l.g.e.a. which anastomoses with a branch of the hepatic artery.